This invention relates to a proximity switching device of the type including a high frequency oscillating circuit and, more particularly, to an output circuit thereof.
A well known proximity switching device comprises an oscillating circuit including a detection coil, a signal producing circuit for producing a detection signal in response to the amplitude of the oscillating circuit, and an output circuit for producing an output signal in response to the detection signal. The output circuit is composed of a NPN transistor or PNP transistor. A load such as an electromagnetic relay is connected between an output terminal and a source terminal when a NPN transistor is used, while the load is connected between the output terminal and a ground terminal when a PNP transistor is used.
It is also known that a complementary transistor pair, consisting of a PNP transistor and a NPN transistor, is used in the output circuit. For example, an emitter of NPN transistor is connected to a ground terminal, while an emitter of PNP transistor is connected to a source line, and the collectors of NPN and PNP transistors are both connected to a common output terminal.
The load, of which there are two types and a terminal of which should be connected to a source line or ground depending on the particular type, may be optionally connected between the common output terminal and source terminal or between the common output terminal and ground terminal. Such output circuit including a complementary transistor pair, however, has the disadvantage that a pair of output transistors would undesirably operate simultaneously or entail large power consumption when a resistor or resistors are used in order to preclude the simultaneous operation.
Therefore, it is an object of this invention to provide a proximity switching device comprising an output circuit including a complementary transistor pair which is not simultaneously operative but alternately operative.
It is another object of this invention to provide a proximity switching device which needs less power.
It is another object of this invention to provide a proximity switching device including an output circuit whose saturation voltage is low.
It is a further object of this invention to provide a proximity switching device having at least an output circuit integrated in a semiconductor chip.